The so-called "lost foam" process, involves pouring molten metal into a foamed plastic pattern surrounded by a porous, unbonded said mold. The molten metal vaporizes the pattern and replaces it in the sand before the sand collapses. The solidified metal thus assumes the shape of the foamed plastic pattern and the pattern destruction products escape into the porous mold. The "lost foam" process has been proposed for use in conjunction with both gravity and countergravity poured metal as exemplified by Wittmoser, U.S. Pat. No. 4,085,790, issued Apr. 25, 1987 and Denis, U.S. Pat. No. 4,616,689, issued Oct. 14, 1986, respectively.
Copending U.S. patent application Ser. No. 096,663, entitled "Casting Metal in a Flowable Firmly Set Sand Mold Cavity", filed Sept. 15, 1987, now U.S. Pat. No. 4,754,798, in the name of G. D. Chandley, describes a cating process wherein a disposable pattern (e.g., wax, foam, etc.) is embedded in a lightly-bonded, self-supporting, sand mold having sufficient porosity to receive liquid and vapors generated upon destruction of the pattern. Low temperature heating of the mold/pattern, prior to casting, causes the pattern to become fluid and wick into the pores of the sand mold as well as flow out of the gate and sprue openings in it. Thereafter, metal is cast into the mold using either gravity or countergravity techniques.
The mold-immersion, countergravity casting process, is described in U.S. patent, Chandley et al U.S. Pat. No. 4,340,108, inter alia, and involves sealing a porous, gas-permeable mold in the mouth of a vacuum chamber, immersing the underside of the mold in an underlying molten metal pool and evacuating the chamber to draw molten metal through one or more ingate(s) in the underside of the mold into one or more mold cavities formed within the mold. Chandley et al's mold comprises a rigid, self-supporting, particulate (e.g., sand) mass formed by a shell molding process wherein resin binders (i.e., thermosets) are used to bind the particles together. One such shell molding process is described in U.S. patent, Almond U.S. Pat. No. 4,632,171. Low temperature chemical-curing techniques may alternatively be used to bond the particulates together and commercial systems therefor (e.g., Isocure.sup.R, Alphaset.sup.R, Betaset.sup.R, or Iroset.sup.R processes) are available wherein a bonding resin-precursor-containing particulate is exposed to a promoter (e.g., a catalyzing or reactive gas) to form the binder resin that hold the particles together. In Chandley et al U.S. Pat. No. 4,340,108, a two-part mold (i.e., cope and drag) is formed in separate operations, glued together, and then transferred as a unit to the casting site. These operations require not only separate and costly mold forming and handling equipment, but also consume valuable plant floor space, increase the risk of mold damage and add labor content to the process.
Finally, copending United States patent application Ser. No. 191,544, filed May 9, 1988, entitled "Countergravity Metal Casting", filed concurrently herewith in the name of G. D. Chandley and assigned to the assignee of this invention, describes a mold-immersion type contergravity casting process wherein an inherently unstable mass of particulates (i.e., with or without a small amount of binder) form the mold and are held about a vaporizable pattern in the casting chamber of the Chandley et al (i.e., U.S. Pat. No. 4,340,108) type by a pressure differential established between the chamber and the exposed under surface of the mold. Molten metal drawn up into the mold vaporizes and displaces the pattern therein.
It is an object of the present invention to provide an improved method for making molds for mold-immersion type countergravity casting processes, which method eliminates the need for separate mold-making, mold-joining and mold-transfer equipment and associated floor space and labor heretofore required to make molds for such processes. It is another object of the present invention to provide an improved method for making molds for the mold-immersion type countergravity casting process which method more closely integrates the mold-making and casting operations so as to provide a more continuous process and the economies associated therewith. These and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.